Thermal relay



May 6, 1930. A. PRESS 9 1,757,589

THERMAL RELAY Filed Aug. 30, 1920 ATTQRNEY Patented May 6, 1930 UNITED STATES PATENT OFFICE ABRAHAM PRESS, OF WILKINSZBURG, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC 8a MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA THERMAL RELAY Application filed August 30, 1920. Serial No. 407,008.

My invention relates to electrical protective devices and particularly to thermal relays, and it has for one of its objects taprovide a thermal relay comprising electro-ionic actuating means.

Another object of my invention is to provide an electro-ionic thermal relay having a thermal lag corresponding substantially to the thermal lag of the energy-translating device with which it is to be associated and having means for varying the thermal lag of the relay.

More specifically, my invention embodies an electro-ionic valve connected to the circuit of the energy-translating device and an adjustable resistor having a negative temperature coefiicient of resistance connected to said valve.

Referring to the drawing:

The figure is a diagrammatic view of an electric circuit comprising an energy-translating device and a device embodying my invention in combination with a three-electrode-tube amplifier.

The filament or cathode 5 of the electroionic valve 4 is connected in substantially the same manner with regard to the energytranslating device 1, the circuit being closed and interrupted by means of the circuitinterrupting device 3. A three-electrode vacuum tube 9 is provided, the terminal of the plate 10 being connected by means of a conductor 11 to one terminal of the actuating coil 7 of the circuit-interrupting device 3.

he plate 6 of the valve 4 is connected to one terminal of the filament or cathode 12 of the tube 9,,the other terminal of the filament being connected, through an adjustable resistor 13, to a battery 14 which may be of the usual type employed for energizing the filament of such a vacuum tube. A battery 15 is connected to one terminal of the adjustable resistance 13 and has its other terminal connected to the second terminal of the actuating coil 7. One terminal of a grid 16 of the valve 9 isconnected to a movable contact on the adjustable resistor 8 which is made of material which has a negative temperaturecoel'licient of resistance. An adjustable resistor 17 is connected between the grid 16 and the plate 6 which, as stated above, is electrically connected to one terminal of the filament 12.

It is necessary to provide a resistance 17, connected as shown, in order to provide a source of direct-current voltage to energize the grid member 16 of the vacuum tube 9. As long as the current traversing the energytranslating device 1 does not exceed its normal value, the voltage existing between the filament 5 and the plate 6 of the electro-ionic valve is relatively small and only a relatively small current flows from the plate 6 through the resistances 17 and 8 and, through the filament 5, back to the plate 6. Since the plate 6 is at a positive potential with respect to the filamentb, the grid 16 is at a negative potential with respect to the filament 12. When the current traversing the ener ytranslating device 1 and the filament 5 iocomes abnormally high, the voltage operating to cause a current to traverse the resistors 17 and 8 becomes much higher and, after a predetermined time interval, causes the resistance of the active part of the resistor 8 to materially decrease because of the fact that the material in the resistor 8 has a negative temperature coeflicient of resistance. The voltage drop across the active part of the resistor 8 is thus materially decreased and, therefore, causes the grid member 16 of the vacuum tube 9 to have a smaller negative potential with respect to the filament 12. This will operate, in the usual manner, to cause a larger current to flow between the filament 12 and the plate 10 of the vacuum tube 9 which will reach a value sufiicient to cause the operation of the circuit-interrupting device 3 at a predetermined value of the potential applied to the grid 16.

It will be noted that the device embodying my invention provides a relatively simple thermal relay of the electro-ionic type which may be easily provided with means for insuring its thermal lag having substantially the same value as the thermal lag of the translatof my invention, various changes may be made therein without departing from the spirit and scope of my invention and I desire that only such limitations shall be placed 5 thereon as are imposed by the prior art or are specifically set forth in the appended claim.

I claim as my invention: In combination, a thermionic device, means including an adjustable resistor having a negative temperature coefiicient of resistance for controlling the energization of said device, a second thermionic device, means whereby a change in a condition of said first mentioned device produces a greater change in said second device, and a circuit interrupter controlled by said second device.

In testimony whereof, I have hereunto subscribed my name this 12th day of August,

ABRAHAM PRESS. 

